The recent Supreme Court of Canada case Maybin v R, 2010 SCC 24 noted here, highlighted the moral basis for attribution of a sufficient causal connection between D's acts and the harm. The Privy Council has recently referred to the moral dimension of diminished responsibility: Daniel v The State (Trinidad and Tobago)  UKPC 15 at -.
Parliament tends to limit defences and to create new offences. It seems to be engaged in extending the scope of acts for which a person can be held criminally responsible. Whether that legislative activity really reflects community perceptions of what is right can be a controversial question. But the important point is that if the courts are perceived by Parliament to be going wrong, legislation can correct that error. Whatever the common law might say, it is trumped by legislation. This is why courts should not be shy about developing the common law.